Wow, complex question.
PARF is the larger of the two, and closer to us DC-area folks. PARF is a pretty robust faire, with probably the biggest complaint being that half the site is paved. It's hosted at a winery (like VARF, but a full blown faire with permanent structures), so there's wine tastings and the like to do in addition to the regular faire activities.
Pitt is a little smaller, but has a lot of charm. It's a very natural site, with a good portion of it being wooded. I've only been there 2 or 3 times, and it's been a few years, so I'm curious to see how it's changed. My understanding is that they don't have a lot of street-cast (hence their call for volunteer cast), and I think they went through a few years of financial troubles that they're digging out of now (if I recall correctly). But it's certainly a nice little faire, at least as of my last visit.